1). Field of the Invention
The present invention relates to an optical system image sensor operating in structures which may contain media with different spectral transmission characteristics; for example, in vessels containing both crude oil and water, either by rendering all media transparent simultaneously, or, on command, by rendering one or more of the media opaque to allow its detection.
2). Discussion of Related Art
In the oil industry, amongst others, it is necessary to inspect surfaces for cracks, corrosion, scale or other defects or characteristics, to examine welds to establish the integrity of a structure and ascertain the need for repair or replacement. It is desirable to use a single sensor to inspect internal surfaces of structures such as tanks, wells and pipelines containing crude oil and water, and also distinguish between oil and water, without emptying, flushing or cleaning the structure. It is also desirable to inspect surfaces coated with oil or wax in air.
Image sensors operating in structures containing fluids transparent in the visible region of the electromagnetic spectrum such as water are well-known, and disclosed, for example, in EP0846840, EP0264511, and WO0206631.
Operation may be extended to opaque fluids by flushing the vessel with a transparent fluid in the vicinity of the image sensor, and a method for doing this is disclosed in U.S. Pat. No. 4,238,158.
An image sensor operating directly in fluids which are opaque in the visible region of the spectrum but transmit energy at other wavelengths, for example, crude oil, is disclosed in GB2332331B. Transmission in these fluids may be limited, restricting operation of a practical sensor to close range.
The absorption at a given wavelength varies widely for different crude oils, but the general shape of each plot of absorption against wavelength is very similar and transmission “windows” occur at the same wavelengths in the spectrum, as shown in U.S. Pat. No. 5,266,800 which discloses a method for using infrared absorption measurements to discriminate between different crude oils.
As well as discriminating between crude oils, is also possible to distinguish between other fluids by measuring their spectral absorption characteristics, as disclosed in U.S. Pat. No. 4,994,671.
It is an object of the present invention to enable an image sensor to operate within, and also by remote command or autonomous internal control to discriminate between, media such as crude oil and water, which have transmission bands in different regions of the spectrum.